The full set, consisting of the jacket and a pair of Plague trousers, grants access to the incinerator area north of East Ardougne. There's not much there except a respawn point of a Cattleprod, which cannot be obtained without the set. This was worn by Master Fisher before the graphical update on 23 March 2010.
The plague set looks almost identical to Mourner gear. Unlike the Mourner gear, however, this, along with the Plague trousers, cannot be used to enter the mourner hideout during and after Mourning's Ends Part II.
The Plague jacket has thick elbow-length gloves already attached which cannot be removed, thus preventing players from being able to wear another pair of gloves.